A rail head is always subjected to contact friction with wheels of trains and to heavy load. In order to harden the rail head to prevent wear thereof, therefore, a heat treatment is applied to impart a high wear resistance to the rail head.
With a view to reducing the number of joints of rails, it is now the usual practice to butt-weld a plurality of rails having a prescribed length by a flash welding process, for example, to prepare a long rail. However, in a long rail thus prepared by butt-welding the plurality of rails, hardness of the rail head decreases in the butt-welded portion under the effect of welding heat. FIG. 1 is a graph illustrating Brinell hardness of the rail head top in the butt-welded portion of a rail. As is clear from FIG. 1, there is observed a remarkable decrease in Brinell hardness of the rail head top, in a welding heat affected zone within a distance of about 20 mm from the butt-welded face as compared with the other portions of the rail head top not affected by welding heat. When trains pass on such rails, the rail head top in the butt-welded portion wears, is deformed, and is caved in earlier than the other portions along with the increase of train passages. As a result, noise is produced when a train passes on these rails and the train is subjected to vibrations.
Under such circumstances, there is a strong demand for development of an apparatus for preventing, when butt-welding a plurality of rails having a prescribed size, a decrease in hardness from occurring on the rail head in the butt-welded portion affected by welding heat, but no such apparatus has been proposed as far as is known.